Ultraviolet detector systems



J1me 1955 J. B. JOHNSON EI'AL 3,

ULTRAVIOLET DETECTOR SYSTEMS Filed April 19, 1963 FIG. I l8 /7 A 2 EP 2/ IF FIG. IA 22 A I Q 24 t INVENTORS JOHN B JOHNSON BY ALBERT LEEN AGENT United States Patent 3,189,743 ULTRAVIOLET DETECTOR SYSTEMS John B. Johnson, Millburn Township, Essex County, and

Albert Leen, West Caldwell, N.J., assignors to McGraw- Edison Company, Elgiu, 111., a corporation of Delaware Filed Apr. 19, 1963, Ser. No. 274,272 4 Claims. (Cl. 250-835) This invention relates to ultraviolet detector systems using detector tubes of the type described in the Howling Patent No. 3,047,761, dated July 31, 1962, and more particularly, it relates to improved operating circuits for such detector tubes.

This application is a continuation-impart of our pending application Serial No. 8 3,755, filed January 19, 1961, and now abandoned upon the filing Olf this application.

In the above-mentioned parent application it has been described that beneficial results are obtained when the ultraviolet detector tube is operated in an AC. circuit because then the tube is quenched automatically at the end of each half-wave pulse of applied voltage to enable the operating circuit to be designed for maximum power efliciency without limitation as to any quenching problem. Thus, when the tube is subjected to sufiicient incident photon radiation it will fire during each half-cycle of applied voltage as soon as the applied voltage reaches a striking potential and once fired the discharge will continue until the applied volt-age falls below a sustaining value. For a tube with tungsten electrodes and with an ionizing gas of pure hydrogen the striking potential is of the order of 700 volts and the sustaining potential is of the order ot 330 volts.

The present invention resides in the discovery that the afore-stated beneficial results are not due primarily to the applied voltage being A.C. but to the applied voltage consisting of distinct pulses with each pulse rising above a striking potential and falling below a sustaining potential. Such pulsating voltage may be unidirectional and be obtained from an AC. source simply through a half or full-wave rectifier without the use of any filtering.

Further, in accordance with the invention it is found that special advantages can be realized over A.C. operation when a pulsating D.C. voltage is applied across the detector tube. For example, a pulsating D.C. voltage, whether obtained through a halt-wave or full-wave rectifier, causes one electrode to be operated always as cathode, to permit a substantially greater radiation from the source being detected to be focused onto that electrode with a resultant higher sensitivity of response.

Further, in accordance with the invention it is found that there is a tendency for contaminants such as alkali metal atoms to migrate from the glass envelopes to the electrodes and there lower the work function to shift the spectral response of the detector tube into the solar range. These contaminants can however be removed by extending the glow discharge throughout the working reigon of the tube but when this is done there is a tendency for the electrodes to overheat and to emit electrons and cause the tube to lock oni.e., continue to discharge with each applied voltage pulse after the incident radiation has ceased. The advantage of applying alternate half-wave voltage pulses from an AC. source to the detector tube is that each applied voltage pulse can be of greater magnitude to extend the glow discharge throughout the working region without overheating the electrodes by reason of the cooling action taking place during the intermediate off half-cycles of the applied source.

Objects of our invention are to provide simple operating circuits for ultraviolet detector tubes which enable the tubes to be operated with improved efficiency, sensitivity and stability. More particularly, it is an object to provide improved ultraviolet detector systems wherein "ice the detector tubes are operated from an AC. source of potential through a rectifier without the use of any filtermg.

In the description of our invention reference is bad to the accompanying drawings, of which:

FIGURE 1 is a schematic circuit diagram showing an embodiment of our invention in which the detector tube is operated from an A.C. source of potential through a half-wave rectifier;

FIGURE 1a is a graph showing the applied potential across the detector tube in the embodiment of FIGURE 1;

FIGURE 2 is a schematic circuit diagram showing another embodiment of our invention in which the detector tube is operated from an A.C. source of potential through a full-wave rectifiier; and

FIGURE 2a is a graph showing the potential applied across the detector tube in the embodiment of FIG- UERE 2.

The ultraviolet detector tube 10 shown in the figures comprises two tungsten-wire electrodes 11 having intermediate parallel portions 1 1a forming a working region within which the emission of an electron will trigger an avalanche discharge when a striking potential is applied across the electrodes and having semicircular end portions curving away from each other out of the Working region to the ends of which are welded supporting pins 12. By way of example, the supporting pins and tungsten wires may be .050 and .017" respectively in diameter and the spacing between the parallel portions of the wire electrodes may be .040. The tungsten wires, supporting pins and weld joints are electropolished and refined as described in the aforestated Howling patent so that they have smooth surfaces tree of edges, projections or other discontinuities as well as of any contaminants. In this manner the working region is confined to the adjacent parallel portions of the wire eletcrodes and the spectral response of the tube is confined to the ultraviolet range.

The tube is provided preferably with a commercial ultraviolet transmitting glass such as of the borosilicate family, for example, Corning glass No. 9741. The supporting pins 12 are extended through graded glass seals in the base of the envelope. The envelope is pumped to a high vacuum while the tungsten-wire electrodes are heated and is then next filled, for example, with a substantially pure hydrogen to a pressure typically of about ten centimeters mercury to obtain a striking potential of about 700 volts and a sustaining potential of the order of 330 volts. The use of different ionizing gases will change the striking and sustaining potentials.

The embodiment of the invention shown in FIGURE 1 includes an AC. source of applied voltage E having an R.M.S. value of the order of 700 volts, which is obtained :as from a 110 volt cycle power line via a step-up power transformer 16. This AC. voltage source is connected to an operating circuit 17 serially including a half-wave rectifier 18, a current-limiting resistor 19, the detector tube 14) and a utilization device in the form, for example, of an electromagnetic relay 20 shunted by a filter condenser 21. The relay has a pair of contacts 22 for controlling, for example, an alarm circuit 23. The contacts may stand normally open and be closed by the discharge current through the relay when the detector tube is fired.

The voltage pulses E applied across the detector tube 16 in the operating circuit 17 are the unfiltered alternate half-wave cycles of the source voltage E as shown in FIGURE la. Since each applied voltage pulse exceeds the required 700 volts striking potential, the tube will fire during each applied pulse provided it is subjected at the time to incident photon radiation. Once the tube is fired the voltage drop across the tube falls to the sustaining 330 volts as indicated by the dotted line 24 in FIG- URE 10, leaving the applied voltage less 330 volts across the utilization device and the current-limiting resistor. When at the end of each voltage pulse the potential falls below the sustaining value the tube is quenched. This automatic quenching permits the operating circuit to be designed for maximum power transfer to the utilization device. in a DC. circuit, only one electrode ever serves as cathode to permit the ultraviolet flux from the source being detected to be focused thereon for maximum sensitivity of response.

In the aforestated parent application it is described that the migration of contaminants fromthe glass envelope to the electrodes will shift thespectral response into the solar region unless these contaminants are driven oil by ionic bombardment accomplished by extending the glow discharge throughout the working region. The cleaningof the electrodes in this manner may however lead to the electrodes being overheated to a point where electron emission will occur and cause the tubes to lock on. An advantage of operating the detector tube from alternate half-cycle pulses of an A.C.'source of potential is that it permits each applied voltage pulse to be increased to ing circuit is a seriesof successive half-wave 11C. pulse as shown in FIGURE 2a.

This operation of the detector tube 10 from a full-wave pulsating DC. potential preserves the same advantages of greater power efficiency inherent in self-quenching and of greater sensitivity inherent in D.C. operation as are described above in connection with the embodiment of FIGURE 1. Although the full-wave operation does not Further, since the detector tube 10 is operated.

permit the glow discharge to be extended to the sameextent as is the case in halt-wave operation, the lack of cleaning action in full-wave operation is compensated in other respects by the delivery of twice the power to the utilization device, all other conditions remaining the.

same.

The embodiments of our invention herein particularly shown and described are intended to be illustrative and not necessarily limitative of our'invention since the same are subject to changes and modifications without departure from the scope of our invention which we endeavor to express according to the following claims.

We claim: 7

1. An ultraviolet detector system comprising a detector tubehaving electrodes with portions ,inan adjacent relapulse exceeds said striking potential and'falls below said sustaining value to quench the tube, and a utilization device connected to said operating .circuit and responsive to the flow of discharge current through said detector tube when the tube is fired.

2. The ultraviolet detector system set forth in claim 1 wherein said rectifier is of a full-wave type causing successive DC. pulses of potential to be applied across said detector tube.

3. The ultraviolet detector system set forth in claim 1 wherein said rectifier is of a half-wave type causing only alternate half-wave pulses of potential to be applied across the said detector tube.

4. The ultraviolet detector system set forth in claim 3 wherein the alternate half-wave potential pulses applied across said detector tube are adapted to .cause the tube when fired to have a glow discharge extending throughout said working region.

References Cited by the Examiner UNITED STATES PATENTS 2,028,338 1/36 Le Bel 315200 2,901,625 8/59 Friedman et al. 250-833 2,956,168 10/60 Pinckaers 250--83.6

RALPH G. NILSON, Primary Examiner.

ARCHIE R. BORCHELT, Examiner. 

1. AN ULTRAVIOLET DETECTOR SYSTEM COMPRISING A DETECTOR TUBE HAVING ELECTRODES WITH PORTIONS IN AN ADJACENT RELATIONSHIP FORMING A WORKING REGION WHEREIN THE EMISSION OF AN ELECTRON WILL TRIGGER AN AVALANCHE DISCHARGE WHEN A STRIKING POTENTIAL IS APPLIED ACROSS THE ELECTRODES, SAID DETECTOR TUBE BEING QUENCHED WHEN THE APPLIED POTENTIAL ACROSS THE TUBE FALL BELOW A SUSTAINING VALUE, AN A.C. SOURCE OF POTENTIAL HAVING A PEAK VALUE EXCEEDING SAID STRIKING POTENTIAL, A RECTIFIER, AN OPERATING CIRCUIT SERIALLY CONNECTING SAID A.C. SOURCE OF POTENTIAL ACROSS SAID DETECTOR TUBE VIA SAID RECITFIER WITHOUT FILTERING WHEREBY THE DETECTOR TUBE IS OPERATED BY A PULSATING D.C. POTENTIAL COMPRISING DISTINCT D.C. PULSES OF WHICH EACH VOLTAGE PULSE EXCEEDS SAID STRIKING POTENTIAL AND FALLS BELOW SAID SUSTAINING VALUE TO QUENCH THE TUBE, AND A UTILIZATION DEVICE CONNECTED TO SAID OPERATING CIRCUIT AND RESPONSIVE TO THE FLOW OF DISCHARGE CURRENT THROUGH SAID DETECTOR TUBE WHEN THE TUBE IS FIRED. 